(1) Field of the Invention
The present invention relates to the field of pointing and/or directional control devices, and more specifically, to both absolute and relative pointing devices designed to control the positioning and movement of both two dimensional and three dimensional objects.
(2) Prior Art
Pointing devices have been in wide use for sometime now in a variety of applications which in some way require control over the movement and/or positioning of an object. Among other uses, these devices have proved to be particularly beneficial in both the manufacturing and computer industries where the signals output by the devices can be used to control the movement, positioning, and in some cases, the operation of machines and visual images.
Pointing devices are usually classified as either absolute or relative. Absolute pointing devices are those which associate the position of the object with the location of the pointing device itself, whereas relative pointing devices associate the movement of the object with the movement of the device regardless of its position. In some applications, however, a single device can control both the movement and location of the object in addition to the magnitude of its displacement (i.e., speed).
Most pointing devices can be categorized into the following types:
1. Digitizing or Graphics Tablets
These can be either absolute or relative pointing devices which comprise a planar tablet having a surface area divided into distinct grids with sensors placed on the grids in a predetermined pattern for sensing the placement of a usually rod-like pointer (or "pen") held by the user or the finger itself. The location of the device is translated into a specific object position by movement of the pen or finger on the surface of the tablet. Such devices are commonly referred to as "digitizing tablets" when placed on a table-top, or as "touch screens" when placed in front of a monitor screen. Detection is normally accomplished through the use of a plurality capacitive sensors, heat sensors, pressure sensors or electrical sensors which detect contact with the pointer or an electrical output therefrom. Some type of logic means is used to convert the signals generated by the sensors into the X and Y coordinates, or an amount of movement of the pen or finger with respect to the grids of the tablet. Position selection is performed by activating a button either at the tip of the pointer or on the side of the tablet.
2. Joysticks
Joysticks may be used as either absolute or relative pointing devices depending upon its application. These devices consist of a box with a control stem protruding from the center of the box for manipulation by the user's hand. The angular movement and/or position of the stem in any direction is detected by coupling the base of the stem to digital decoders forming X and Y rotational sensors implemented in the bottom of the box. Movement of the stem in any direction causes the rotational sensors to generate electronic vector signals that track the displacement along two axis, while more sophisticated joysticks generate signals which also vary in magnitude with the angular displacement of the stem. The movement of the joystick is normally associated with the movement of an object on a computer screen such as a cursor or an airplane, however, it can also be used to select specific locations on the screen by associating the stem's position with a coordinate position on the screen. Selection is performed by activating one or more buttons located on the stem of the joystick.
3. Mouse/trackball
These are relative pointing devices which measure movement of a sphere disposed either at the bottom of a movable "mouse" housing or on the top of stationary "trackball" housing. The rotational movement of the sphere is mapped to the linear movement of an on-screen object using X and Y rotational decoders. The decoders each comprise a roller disposed orthogonally with respect to each other and in constant contact with the surface of the sphere. Each sensor further comprises an axle connecting the roller to a slotted disk and optical sensors placed proximate to the disk for detecting the rotational and directional displacement of the radial slots as the sphere is moved. The optical sensors have their outputs coupled to signal generation circuitry within the housing of the mouse or trackball for conversion of the displacement into digital signals. Again, selection is performed by activating one or more buttons on the housing of the device.
When these pointing devices are used in conjunction with a computer system, they are usually physically separated from the main component housings but connected thereto via a serial cable. In the more recent "notebook" type computers, however, these devices are often incorporated within the computer's keyboard housing. In this manner, a mouse, trackball or small joystick can be made integral with the surface of the keyboard to facilitate operation of the device by reducing the distance the user must traverse with his hand to reach the device. Furthermore, these devices may alternately be implemented in a base pivotally attached to the side of the keyboard so as to reduce the overall surface area of the keyboard.
Although pointing devices implemented as an integral element of a keyboard housing help to minimize the distance the user must traverse his hand between the keys and the device, each of the above described pointing devices still requires the user to remove his fingers from the keys and reposition his hand over the device in order to manipulate it and activate the command buttons. Hence, a major drawback with such devices is that they require the user to interrupt his typing activity to manipulate the device, thereby hindering his typing ability and causing excessive fatigue to his wrist.